Moloney murine sarcoma virus (M-MSV) is a replication-defective retrovirus that transforms fibroblasts in vitro. It has been demonstrated that M-MSV arose by recombination between the replication-competent Moloney-MuLV and a specific subset of cellular sequences. These sequences present in M-MSV are known to be involved in cellular transformation mediated by the virus. The purpose of this work is to identify the messenger RNAs of M-MSV involved in the cellular transformation. The study will be focused on those RNAs coded for by different clones of M-MSV deletion mutants. Total cellular RNA from nonproducer transformants will be analyzed by the "Northern gel technique" and the M-MSV specific RNA detected by molecular hybridization. The sequence organization of these viral RNAs will be characterized by utilizing specific (32P)-labeled M-MSV DNA probes corresponding to specific regions of the viral genome. Eventually the putative translational products of such an RNA molecule will be analyzed.